Make Efficient Grass For Large Areas In The BGE
I believe you have to rely on intersecting textured planes for this. The grass model with 24 tris is way too much (i am assuming actual strands). Additionally you have to "grow" the grass only in the player visible area, and cull it when it gets really far away and substitute with a similar ground texture (even triple A games do this, like Skyrim). Additionally don't forget to have a fustrum size of your sun lamp that doesnt cover the entire landscape, but moves with the player. Drawing shadows is very expensive.

There are more than a few tutorials on how to create good looking grass patches for all kinds of game engines and the underlying principles stay the same for BGE unless the engine uses their own custom grass system.

Here is a tutorial for 3ds max on how to do grass for UE4: https://www.youtube.com/watch?v=B4j5tzAIflU

Here is one in blender (very similar): 
https://www.youtube.com/watch?v=BKxUKzpx--s

And here is a demo of an implementation of a generative approach in BGE: https://www.youtube.com/watch?v=kN6ftu0H4bQ

You might also want to have a look at different BGE forks like Upbge (https://www.youtube.com/watch?v=fx9JfJyCY6I) and Armory Engine (for better performance in transparency mixing and low poly meshes etc)